1. Field Of The Invention
This invention relates to recirculating roller bearing assemblies, and more particularly relates to a linear recirculating roller bearing assembly of the type including a plurality of rollers disposed in a predetermined side-by-side spaced relationship on a chain for rolling recirculating movement along substantially parallel, spaced apart, load bearing and return surfaces.
2. Description Of The Prior Art
A typical chain-type, linear recirculating roller bearing assembly is disclosed in Anderson U.S. Pat. No. 3,111,350. The roller bearing assembly includes a bearing block having a load bearing surface recessed in a linear track or race, and an unloaded surface recessed in a return track. A chain is mounted on the bearing block, and a plurality of cylindrical rollers is mounted on the chain in parallel, side-by-side relationship. The rollers rotate on the chain and recirculate over the linear tracks formed in the block.
One of the major disadvantages of known forms of chain-type linear recirculating roller bearing assemblies, such as the assembly disclosed in the above-identified Anderson patent, is that the rollers have a tendency to skew from their linear track. This is caused chiefly when the rollers return to the working loaded track from the unloaded return track, and the load which they pick up is not distributed evenly over the length of the rollers. Thus, one end of the roller carries a greater load than the other end and causes the less loaded portion to rotate. As a result, the rollers deviate from the linear track and contact the sidewalls of the bearing block defining the raceway, causing wear to the sidewalls and to the rollers.
The rollers will also skew if they have a non-uniform diameter over their axial length. For purposes of explanation, such rollers may be imagined as being formed with a frusto-conical shape. These rollers have a tendency to follow a circular or non-linear path when in rolling motion. Furthermore, a dirt particle picked up by a roller may impede its rolling motion and also cause the roller to skew from its linear track. The force required to return the roller to a proper linear path is considerable. For example, a typical roller can carry a 4,500 lb load distributed over its length. If the coefficient of friction between the roller and the bearing block is typically 0.2, then a static frictional force of 100 lb would have to be overcome to return the roller to its, proper linear path.